This invention relates to refrigeration apparatus and a refrigeration process and a process employing a mixture of different refrigerants.
Refrigeration systems are well known which employ a single refrigerant, for example, CFC refrigerants such as R-12 and HCFC refrigerants such as R-22. These refrigerants, however, have serious environmental drawbacks and are being replaced by refrigerants of the HFC type such as R-32, R-125 and R-134a in different combinations.
The individual HFC refrigerants have diverse characteristics, as shown in the following table:
In many refrigeration systems, the following characteristics are preferred:
Densityxe2x80x94heavy
Boiling Pointxe2x80x94low at evaporator and high at condenser
Latent Heatxe2x80x94large
Condenser Pressurexe2x80x94low
Evaporator Pressurexe2x80x94high
Heat Transferxe2x80x94good
Flammabilityxe2x80x94no
In the above, hfg is the enthalpy difference between 100% vapor and 100% liquid.
R-32 is a preferred refrigerant because of its high latent heat and high evaporator pressure, which reduces the compressor work and thus the compressor size. That is, the compressor work WCOMPRESSOR is defined as:
WCOMPRESSOR=∫vdP 
where v=specific volume=1/density; and P=pressure.
The compressor work in a typical refrigeration system can be simplified for an isentropic process as:   W  =                    kRT        1                    k        -        1              ⁡          [                                    (                                          P                2                                            P                1                                      )                                              (                              k                -                1                            )                        /            k                          -        1            ]      
where k is a specific heat ratio, R is a gas constant, and T is temperature. As depicted in the above equation, the compressor work can be reduced by reducing the pressure differential, P2xe2x88x92P1 or compression ratio, P2/P1. As the compressor work is reduced, the EER (energy-efficiency ratio) increases because EER is defined as the ratio of the heat absorption at the evaporator to compressor work.   EER  =            Heat      ⁢              xe2x80x83            ⁢      absorption      ⁢              xe2x80x83            ⁢      from      ⁢              xe2x80x83            ⁢      evaporator              Work      ⁢              xe2x80x83            ⁢      done      ⁢              xe2x80x83            ⁢      by      ⁢              xe2x80x83            ⁢      compressor      
In a typical system, as evaporator pressure increases, the pressure change in the compressor is reduced, thus reducing the compressor work.
While R-32 has the best thermal characteristics, it is more flammable than the others, and carries with it the danger of fire. Consequently, R-32 is commonly mixed with non-flammable fluids such as R-125 and R-134a to reduce the fire danger.
Currently available mixture refrigerants include R-407c and R-410a. The former (R-407c) is one of the R-407 series refrigerants, which include R-407a, R-407b, R-407c, etc. The R-407 series is made of three refrigerants R-32, R-125 and R-134a. The last letter in the designation of R-407 indicates different composition ratios of R-32, R-125 and R-134a. For example, R-407c is made of R-32, R-125 and R-134a at a ratio of 23:25:52 based on mass. Similarly, R-410a is one of the R-410 series refrigerants, which are made of two refrigerants R-32 and R-125. The last letter xe2x80x9caxe2x80x9d in R-410a indicates that a composition ratio of R-32 and R-125 is 50:50 by mass. Depending on the composition ratio, the last letter can vary.
Several new HFC type refrigerants such as R-134a, R-407c and R-410a have been developed as attempts to optimize the trade-off of flammability versus thermal efficiency. The first R-134a has replaced R-12 for automotive air conditioners, refrigerators and large chillers. This refrigerant has relatively poor heat transfer characteristics but in a typical system produces a pressure of about 8 atm at the evaporator and 16 atm at the condenser. Thus, the relatively small xcex94P at the compressor produces excellent efficiency. Therefore, this refrigerant has replaced R-12 for many applications, despite its poor heat transfer characteristics.
A second HFC type refrigerant is R-407c, which is a mixture of R-32, R-125 and R-134a in proportions of 23:25:52 respectively. This mixture, however, produces only about 6 atm at the evaporator and 20 atm at the condenser (like R-22) and has poor heat transfer characteristics due to the high proportion of R-134a.
A third HFC type refrigerant is R-410a, which is a mixture of R-32 and R-125 in a ratio of 50:50 respectively. This mixture, however, produces about 12 atm at the evaporator, but 30 atm at the condenser and requires a large compressor and compressor work.
It would be very desirable to provide a novel refrigeration system, which would permit the use of an non-flammable mixture of refrigerants, a reduced condenser pressure and an increased evaporator pressure; and which takes the best advantage of the properties of the individual fluids of the mixture.
In accordance with the invention, a novel system and refrigeration process is provided in which the composition of the refrigerants is controlled as the thermal load of the refrigeration system changes with the help of a vortex generator and a storage tank. For example, for the case of R-407c, the density of R-32 is substantially smaller than those of R-125 and R-134a such that R-32 is separated from the R-125 and R-134a using the centrifugal force in the vortex generator. Once R-32 is separated, it can be stored in a storage tank for the low-thermal load operation. In the low thermal load operation, one can take benefits of the preponderance of R-134a, which is low condenser pressure and high EER (energy-efficiency ratio). For the case of a high thermal load operation, R-125 and R-134a, instead of R-32, can be stored in the storage tank such that one can take benefits from the preponderance of R-32 in the system, which is a high cooling capacity.
Co-pending application Ser. No. 09/608,656 filed Jun. 30, 2000 (P/3746-2) describes a novel system and refrigeration process in which a first component (for example, R-134a) is recirculated in the condenser while the other component or components (for example, R-32 and R-125) are directed, without recirculation, to the evaporator to increase evaporator pressure and heat capacity. The component of the circulating refrigerant may be controlled, as by a valve, in the recirculation path to effectively control thermal load variation.
According to a first aspect of the present invention, there is provided a refrigeration system comprising a compressor, a plurality of condensers, positioned in parallel, each having an input and an output, an expansion device, an evaporator, said compressor, said condensers, said expansion device, and said evaporator being connected in a closed circuit and being operative to circulate a refrigerant fluid comprised of a first component having a first density and a second component having a second density, a separator having an input connected to an output of said compressor and outputs connected to the inputs of said condensers, a storage tank, a plurality of first valves selectively connecting the outputs of the condensers as inputs to the storage tank, and a second valve operative to selectively feed the contents of the storage tank into the closed circuit.
According to a second aspect of the invention, there is provided a refrigeration system comprising fluid compressor means, a plurality of fluid condenser means, positioned in parallel, each having an input and an output, fluid expansion means, evaporator means, said compressor means, said condenser means, said expansion means, and said evaporator means being connected in a closed circuit and being operative to circulate a refrigerant fluid comprised of a first component having a first density and a second component having a second density, fluid separator means having an input connected to an output of said compressor means and outputs connected to the inputs of said condenser means, fluid storage means, a plurality of first valve means selectively connecting the outputs of the condenser means as inputs to the storage means, and second valve means operative to selectively feed the contents of the storage means into the closed circuit.
In a preferred embodiment of the present invention, a vortex generator is used as the means to separate one refrigerant from the other refrigerants. The vortex generator is located between a compressor and condenser. The condenser is divided into two parallel sections. The vortex generator has two outlets, each outlet is connected to the inlet of each condenser such that the light refrigerant (i.e., R-32) enters the condenser-1, whereas the heavy refrigerant(s) enter(s) the condenser-2. Using two three-way valves, the liquid refrigerants from the two condensers can be either stored in the storage tank or sent to an expansion valve.
Once the control of the composition of the mixed refrigerants is completed depending on the high or low thermal load condition, the superheated refrigerant vapor from the compressor bypasses the vortex generator using a three-way valve, and the refrigeration continuously operates with substantial energy savings.
1. The vortex generator, or the like, between compressor and condenser sections will separate R-32 from R-125 and R-134a using the centrifugal force produced by the vortex flow;
2. A three-way valve located at the end of each condenser directs the liquid refrigerant to either the storage tank or the expansion valve, depending on the high or low thermal load;
3. Once the desired composition of the refrigerant mixture is obtained, both the vortex generator and storage tank are isolated (or bypassed) from the operation of the refrigerant system until the changes in thermal load require a new composition of the refrigerants.
In the novel system, the separation of refrigerants is performed using the centrifugal force created by the vortex flow. Other devices that can generate the centrifugal force can be used, including a cyclone.
The advantages produced by the invention include:
1. The use of an non-flammable fluid;
2. A large heat capacity at evaporator;
3. A lower condenser pressure;
4. A higher vapor pressure in the evaporator, producing a lower specific volume v in the evaporator, thus reducing compressor work ∫vdP.
As a result of the above, the system requires lower compressor work to reduce compressor size, and produces higher latent heat in the evaporator, producing a more efficient evaporator. Furthermore, the refrigeration system in the invention replaces the usual ON/OFF operation of the compressor with the composition control of the mixture refrigerants, thus substantially reducing the energy loss due to the ON/OFF operation. Also, the refrigeration system in the invention eliminates the need of an expensive invertor compressor and associated loss in the EER. The refrigeration system in the invention can produce substantial energy savings and increase SEER (system EER) with the composition control using a constant-speed compressor.